Epigenetic mechanisms control many normal and diseased state processes. In this proposal we will use herpes simplex virus 1 (HSV-1) as a probe of the epigenetic mechanisms operative in normal and diseased oral epithelial cells. Our specific aims are: 1. To define the mechanisms of epigenetic regulation of HSV-1 gene expression in normal oral keratinocytes. We will first define the baseline mechanisms of epigenetic regulation of HSV gene expression in immortalized normal human oral keratinocytes (NOK cells), define the kinetics of chromatin and heterochromatin association with viral lytic genes in oral keratinocytes, define the host chromatin factors that positively and negatively regulate viral gene expression in NOK cells, and test the ability of drugs that target chromatin factors to synergize with traditional herpesviral drugs. 2. Test the hypothesis that HSV-1 infection can be used as a probe of epigenetic mechanisms in different oral disease states. Epigenetic mechanisms are altered in HIV-infected oral epithelial cells, in anti-retroviral treated cells, and in tumor cells. We have found that HSV-1 infection can be used as a probe of osteosarcoma cells to identify novel epigenetic mechanisms that are operative in these cells. Therefore, we will test if HSV-1 infection can identify altered epigenetic mechanisms in diseased oral cells. In this Aim we will define the epigenetic mechanisms in oral epithelial cells from HIV+/anti-retroviral treated individuals versus HIV- individuals and in oral epithelial cells treatd with HIV protease inhibitors, and define the epigenetic mechanisms operative in oral tumor cells. 3. To define the effect of oral disease states on IFI16 nuclear sensing of HSV DNA. We have shown that in normal human cells including oral keratinocytes that the nuclear IFI16 DNA sensor is required for induction of IFN- and interferon-stimulated genes and for host silencing of HSV IE. In this Aim we will determine if IFI16 sensing of HSV DNA is altered in oral keratinocytes from HIV+/anti-retroviral treated individuals versus HIV- individuals, and in oral epithelial cells treated with HIV protease inhibitors. In this aim we will determine if IFI16 sensig of HSV-1 DNA is altered in oral tumor cells. These studies on epigenetic regulation of HSV-1 gene expression have the potential of defining new mechanisms of viral infection and disease in oral epithelial cells and new antiviral strategies. Furthermore, the studies will provide new mechanisms for identifying oncogenic mechanisms and therapies for oral cancers.